Impact of the internet and scholar age distribution on academic citation age

sulting in the use of more recent citations, the Internet appears to have lengthened the average life of academic citations by 6 to 8 months. The aging of scholars seems to have a greater impact, accounting for 2.8% of the variance for the sciences and 0.9% for the social sciences. However , because the diffusion of the Internet and the aging of the professoriate are correlated over this time period, differentiating their effects is somewhat problematic. Citations to academic materials are generally understood to increase over time as the cited publications are distributed. The number of citations to a given publication continues until it reaches a maximum, at which point it begins to decline as the document's information becomes increasingly obsolete. Eventually, the number of citations to a given set of articles at a given time approaches zero, with references to older literature being made only to publications that have been defined as classic. The research literature on the changes in the use of academic publications over time, its growth and age, and the mathematical models used to describe this process have been reviewed in detail by Line and Debus proposed a mathematical model that describes the aging process of academic citations. The model was adopted from the pharmacokinetics literature that was used to describe drug concentrations in the blood, which also is a process that starts at or near zero, increases, and then approaches zero as time increases and unknown to Barnett and colleagues, Avramescu (1979) proposed a mathematically identical model to describe citation obsolescence. The Barnett et al. model is retrospective: It describes how a given set of citations makes use of the available literature from the same year, 1 year previous, 2 years before, and so on. To control for the annual growth in the number of articles (Egghe & Rousseau, 2000b), citation information is treated as proportions; that is, the model predicts the proportion of citations by current articles to past articles. The Barnett et al. (1989) model assumes that at a given time, t, there are four pools of published articles: (a) a pool consisting of articles published, but not cited or disregarded (a pool of " unripe " articles): the x(t) pool; (b) a pool of cited articles: the y(t) pool; (c) a pool of articles that have been cited, but are now out of date or otherwise irrelevant to existing scholars: the z(t) …